The embodiments described herein relate generally to X-ray computed tomography and, more particularly, to imaging thin objects using X-ray computed tomography.
In at least some known computed tomography (“CT”) imaging systems, an X-ray source projects a fan-shaped or a cone-shaped beam towards an object to be imaged. The X-ray beam passes through the object, and, after being attenuated by the object, impinges upon an array of radiation detectors. Each radiation detector produces a separate electrical signal that is a measurement of the beam intensity at the detector location. During data acquisition, a gantry that includes the X-ray source and the radiation detectors rotates around the object.
In restricted areas such as airports and correctional facilities, detecting contraband (e.g., explosives, drugs, weapons, etc.) in objects is a high priority. At least some known contraband detection systems utilize CT technology to produce CT images and detect contraband in objects such as luggage, packages, containers, etc. CT volume scanners acquire a plurality of cross-sectional CT slices of an object at regular, closely spaced intervals so that the entire volume of the object is imaged. Each pixel in each CT slice therefore represents a volume, and is referred to as a voxel. The value, or CT number, of each voxel represents an approximation of the density of the material within the voxel. Each voxel represents X-ray attenuation and is related to object density and effective atomic number. Many volume scanners employ multiple rows of detectors arranged in an array, and the object is moved continuously through the gantry while the gantry rotates. Once the object is imaged, the generated image may be analyzed to determine whether the object contains contraband.
At least some known CT scanners can accurately produce CT numbers for large objects. However, as objects become smaller and/or thinner, the accuracy of the CT number may decrease, as the accuracy of the CT number is limited by the spatial resolution of the scanner and the size of the pixels or voxels. Accordingly, when imaging relatively thin objects, the image data acquired using at least some known CT scanners is relatively noisy and can lead to poor segmentation. Further, physical distortions such as nonlinear particular volume, beam hardening, Rayleigh scatter, and other effects may impair the quality of the generated images. Therefore, at least some known CT systems are unable to clearly and accurately image thin objects, increasing the difficulty of identifying contraband in such objects.